1. Field of the Invention
The present invention relates to a track cross signal generation circuit, more particularly, to a track cross signal generation circuit for an optical recording medium used in an optical disk device, for generating a track cross signal, i.e., a track zero cross signal indicating tracks crossed by a beam, by using a tracking error signal.
2. Description of the Related Art
Recently, optical disk devices using an optical disk or magneto-optical disk, have been studied and developed as a large capacity storage (mass storage device), and an optical beam has been used to carry out a write operation, erase operation, and read operation therein. In the optical disk devices, an optical beam crosses tracks of an optical recording medium (optical disk, or magneto-optical disk) during a seek operation. This crossing movement provides a tracking error signal for a comparator, which generates a track zero cross signal in accordance with the tracking error signal. Based on the track zero cross signal, a track counter in which the number of tracks up to a target track is set and counted down, and when the counter reaches zero, it is determined that the target track has been reached.
During the seek operation, a target speed for controlling the speed of the beam is set in accordance with the number of tracks left in the track counter. The beam speed is also controlled by detecting the beam speed in accordance with the track zero cross signal.
The track zero cross signal is generated in accordance with the tracking error signal whose offset has been compensated in an offset compensation circuit. An example of the offset compensation method of the tracking servo system in the optical disk device is disclosed in Japanese Unexamined Patent Publication (Kokai) No. 2-166633.
Note, the frequency band of the offset compensation circuit is lower than the maximum frequency of the tracking error signal in a high-speed region of a beam during the seek operation, the gain of the tracking error signal is not sufficient in the high-speed region of the seek operation to correctly detect track crossings of the beam.